Polybutylene terephthalate, ABS resin, etc. are in wide use in electric and electronic parts, machine parts, automobile parts and other applications, for their excellent properties. These thermoplastic resins, however, are inherently flammable and accordingly their application fields are restricted. Hence, a halogenated polycarbonate oligomer was proposed as a flame retardant for said resins.
In order to impart fire retardancy to a thermoplastic resin, it has conventionally been necessary to mix a thermoplastic resin ordinarily of pellet or chip form with a fire retardant and, as necessary, other additives and melt-extrude the resulting mixture by the use of an extruder to obtain a fire-retardant thermoplastic resin of pellet form. However, the above fire retardant is a very fine powder, and accordingly this invites poor processability such as generation of layer separation and bridging at the hopper portion of extruder, insufficient biting by the screw portion, and the like; as a result, the fire retardant has a drawback in that its uniform mixing is difficult and the final product obtained has low quality. Further, the fire retardant has a drawback of poor workability; for example, the fire retardant becomes dust by itself, significantly deteriorating the working environment. Furthermore, the fire retardant contains a considerable amount of the solvent (methylene chloride) used in the production thereof, and there is a fear that the solvent may adversely affect the quality of the final product obtained. In order to improve the above-mentioned poor processability and workability, Japanese Laid-Open Patent Publication No. 149738/1987 proposes a granulation method wherein a halogenated hydrocarbon type fire retardant is cold-powderized under pressure. However, to granulate a halogenated polycarbonate oligomer by the above granulation method employing cold powderization under pressure, there are drawbacks in that a large pressure of 100-2,000 kg/cm.sup.2 is required and further the granules obtained are easily disintegrated during transportation or working.